(1) Field of the Invention
The present invention relates to a method used to fabricate semiconductor memory devices, and more specifically to a method used to define a metal contact plug structure, and an overlying metal interconnect structure, using a two step, in situ etch procedure.
(2) Description of Prior Art
The trend to continually shrink the dimensions of memory chips, necessitates the use of more sophisticated structures, used for contact to underlying conductive regions, in a semiconductor substrate, and used to contact and communicate with overlying metal interconnect structures. A conductive metal plug structure, usually comprised of tungsten, or doped polysilicon, has been used for these purposes. The metal plug is formed in a contact hole, in an insulator layer, with the metal plug overlying, and contacting, a conductive region in the semiconductor substrate, such as a source/drain region of a metal oxide semiconductor field effect transistor, (MOSFET). The procedure used to create metal plugs can however prove difficult to control. For example, microloading effects, or variations in the reactive ion etching, (RIE), removal rate of a specific metal, employed to remove unwanted metal from the top surface of an insulator layer, while forming the metal plug in a contact hole in the same insulator layer, can result in an overetching of metal, in areas in which the density of contacts holes is large, while leaving unwanted metal still remaining on the top surface of the insulator region, in non-dense regions. Therefore when attempting to clear unwanted metal, in non-dense regions, overetching of the metal plug, and of the adhesion and barrier layers, used between the metal plug, and the sides of the contact hole, can occur in the dense regions. The result of recessed metal plugs, and removed adhesion and barrier layers, can degrade yield, or result in reliability problems.
This invention will offer a process in which a metal plug is formed without subjection to either a RIE or a chemical mechanical procedure, for definition of the metal plug. This invention features the deposition of the adhesion and barrier layer, as well as the in situ deposition of the metal, completely filling the contacts holes. However prior to definition of the metal plug, an overlying metal interconnect layer, and an anti-reflective coating, (ARC), are deposited. After patterning of the ARC and metal interconnect layer, via photolithographic and selective anisotropic RIE procedures, using a first etch chemistry, with the selective RIE procedure stopping on the metal plug layer, the etch chemistry is changed, and a second selective RIE procedure is performed, using a second etch chemistry, to define the metal plug, using the same photoresist shape as a mask. This novel procedure results in the in situ definition of a metal interconnect structure, larger in width than the width or diameter of the contact hole, now embedded with the metal plug, and also results in the definition of a metal plug structure, formed without directly exposing the metal plug, in the contact hole, to the patterning procedure. Prior art, such as Tabara, in U.S. Pat. No. 5,767,015, describes a method for forming a metal plug structure, but does not show the present invention, in which an in situ RIE procedure is used for definition of both a metal interconnect, and a metal plug structure, without directly exposing the metal plug structure, in a contact hole, to the RIE procedure.